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318 Onan P218 - Rebuild or Repower?


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109 replies to this topic

#16 Texas Deere and Horse OFFLINE  

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Posted September 22, 2011 - 03:20 PM

Lawnguy, You could only need to do a valve guide job and re-ring it.

#17 olcowhand ONLINE  

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Posted September 22, 2011 - 03:54 PM

Dial gauge the mains, plastigauge the rods. If within spec, don't mess with them. Likely the valve guides are worn, so they and the valves may need replaced. All this can be measured to know which way to go. But if this engine ran well but only smoked, I would not do a re-power unless you just wanted to. The most I've ever put into an Onan to get them running great with no smoke, and reliable was a bit over $300, with no labor (me doing all work myself).

#18 Lawnguy OFFLINE  

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Posted September 23, 2011 - 05:21 PM

Yes, the engine ran great, and hopefully I can get away with new seals & rings. I was able to borrow a spring compressor and not ever doing this before, was able to figure the tool out. After compressing the spring the cap fell out (picture 1) and then I took a screwdriver and magnent to pull the keepers off. I acually didn't need the screwdriver, the magnent pulled them right off. As far as the seals go (picture 2), I'm not sure how to remove them, so would like some advise on that.

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#19 Lawnguy OFFLINE  

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Posted September 23, 2011 - 05:31 PM

Lots of build up in the intake (the big valve right?) (picture 1) The other side of the motor showed hardly any signs of this. Even the valve itself (picture 2) had a ton of buildup. I forgot to bring my calipers home from work, but if they spec out okay, will my wire wheel on my bench grinder be okay to clean them up?

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#20 trowel OFFLINE  

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Posted September 23, 2011 - 05:45 PM

If you use the soft brass ones carefully, you don't want to round over the lip, i would soak it in some kind of penetrating oil or ATF first then try it carefully if the crud is still there,
after cleaning i would do well to advise you to lap in the valves,

#21 trowel OFFLINE  

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Posted September 23, 2011 - 05:49 PM

Oh, and carfull when scraping the intake and exhaust ports avoiding the seats and engine deck, a dremel tool with a soft wire brush or pipe cleaning wire brushes works great for ports,

#22 Lawnguy OFFLINE  

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Posted September 26, 2011 - 05:53 PM

Worked on the motor a little bit more tonight. I popped the valve seals off with a flat blade screwdriver (picture 2) took alittle bit of prying, but came right off. I then got the dremmel out and cleaned out the intake and exhaust ports. I used the steel wire one first to get the rough stuff off, then switched to the brass which acualy worked better, but both wore down pretty quickly, so will have to buy a couple more to clean the other side (picture 1) an earlier post suggested I change the valve guides out, so will need some suggestions on how to get them out? Thanks!

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#23 Lawnguy OFFLINE  

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Posted September 26, 2011 - 06:02 PM

I then cleaned all four valves on my bench grinder that has a soft wire wheel on it. I did use a screwdriver to scrape some of the crud off first, but was carefull not to get near the seat area. oh, I marked the cylinder and valves with red tape on once side, thinking I should put the same valve back in the same port when reassembling. I then checked with the caliper at various place's on the valve and also twisting the valve to see if there were any high or low spots. All four came out to .279 I'm not sure if that is within spec (haven't checked yet). but thought that was pretty good that all four valves. If anyone know's if this is okay please let me know. thanks!

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#24 docauto OFFLINE  

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Posted September 26, 2011 - 06:44 PM

It is good to find this thread because I will be doing the same thing this winter & this will be my first lawn tractor restore project. Thanks for sharing!

#25 olcowhand ONLINE  

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Posted September 26, 2011 - 06:54 PM

Valve stems minimum .2780" - max .2785". Being you got a larger measurement, likely just the caliper off a tick. Also, being all measure the same, the valves are likely good to go. I just used my lathe to turn a valve guide too that both knocks the old ones out, and drives the new in. I'll take a pic later if you like of the tool, but it's simple, just a bolt turned down on the end to fit snug into the hole in the guide, then the rest of it just slightly under the total diameter of the guide. Having the pilot inside the guide prevents peening the hole in the guide smaller when installing it.

#26 Lawnguy OFFLINE  

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Posted September 28, 2011 - 06:05 PM

Decided to check the end play of the valves with a dial gauge just to be sure if valve guides need replacment or not. It was a little tricky since the gauge didn't have the attachments I needed to measure the valve as close to the seat as possible. I measured the intake valve first by pulling and pushing the valve and watching the dial. It was averaging between .005 and .007" I think the max is .003" so looks like I will need to replace the guides. The exhaust valve was slightly better at .003" to .005"

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#27 Lawnguy OFFLINE  

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Posted September 28, 2011 - 06:12 PM

I also removed the rings from the piston and inserted them one at a time into the cylinder to take some measurements. I then measured the gaps. Ring #1 measured .006" with a feeler gauge and ring #2 measured .023" Ring #3 which I think is the oil ring? I had to use my calipers on that which measured .124" I'll need some feedback on this one as to weather that is cosher or not?

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#28 mikebramel OFFLINE  

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Posted September 28, 2011 - 09:02 PM

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Edited by mikebramel, September 30, 2011 - 12:25 AM.


#29 Lawnguy OFFLINE  

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Posted September 29, 2011 - 02:37 PM

Valve stems minimum .2780" - max .2785". Being you got a larger measurement, likely just the caliper off a tick. Also, being all measure the same, the valves are likely good to go. I just used my lathe to turn a valve guide too that both knocks the old ones out, and drives the new in. I'll take a pic later if you like of the tool, but it's simple, just a bolt turned down on the end to fit snug into the hole in the guide, then the rest of it just slightly under the total diameter of the guide. Having the pilot inside the guide prevents peening the hole in the guide smaller when installing it.


Once I create the tool for taking out the guides, will it help to heat that area up or do they come out easy enough without it? thanks.

#30 Lawnguy OFFLINE  

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Posted October 06, 2011 - 12:18 PM

Removed all the valve guides this week. I took a 5/16" x 3" bolt and took it to my bench grinder until it slid into the valve guide opening. I then rounded off the nut so it wouldn't score the side of the guide bore (pic 1). After a few hits with my hammer, it slid off the bolt and took a little meat off my finger. Yeah it hurt....lol The first few hits of the hammer have to be hard, but once it started moving I could tap it out after that (pic 2) Oh! Don't forget to remove the lifters before you start or you won't get either one of them out. Going to order the new guides this week, 110-3526 intake, and 110-3527 exhaust. I got a good price on the intake seals 509-0289 for $7.95 for the pair.

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